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Published December 16, 2013 | Published
Journal Article Open

Calibration of sealed HCl cells used for TCCON instrumental line shape monitoring

Abstract

The TCCON (Total Carbon Column Observing Network) FTIR (Fourier transform infrared) network provides highly accurate observations of greenhouse gas column-averaged dry-air mole fractions. As an important component of TCCON quality assurance, sealed cells filled with approximately 5 mbar of HCl are used for instrumental line shape (ILS) monitoring at all TCCON sites. Here, we introduce a calibration procedure for the HCl cells which employs a refillable, pressure-monitored reference cell filled with C_2H_2. Using this method, we identify variations of HCl purity between the TCCON cells as a non-negligible disturbance. The new calibration procedure introduced here assigns effective pressure values to each individual cell to account for additional broadening of the HCl lines. This approach will improve the consistency of the network by significantly reducing possible station-to-station biases due to inconsistent ILS results from different HCl cells. We demonstrate that the proposed method is accurate enough to turn the ILS uncertainty into an error source of secondary importance from the viewpoint of network consistency.

Additional Information

© 2013 Author(s). This work is distributed under the Creative Commons Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 17 July 2013. Published in Atmos. Meas. Tech. Discuss.: 5 August 2013. Revised: 8 November 2013. Accepted: 12 November 2013. Published: 16 December 2013. We would like to thank the head of the workshop at KIT IMK-ASF, A. Streili, for his exceeding commitment with the construction of the 40 cm cell bodies. We acknowledge support by the European integrating activity project InGOS (www.ingos-infrastructure.eu) for performing this study. BIRA thanks the Belgian Federal Science Policy for support through the AGACC-II project. The LPMAA is grateful to the French INSU LEFE programme for supporting the TCCON-Paris project. Part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. We acknowledge support by Deutsche Forschungsgemeinschaft and Open Access Publishing Fund of the Karlsruhe Institute of Technology. The service charges for this open access publication have been covered by a Research Centre of the Helmholtz Association. Edited by: D. Griffith

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August 22, 2023
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